Doped nickelate compounds

ABSTRACT

The invention relates to novel materials of the formula: A 1-δ M 1   V M 2   W M 3   X M 4   Y M 5   Z O 2  wherein A is one or more alkali metals comprising sodium and/or potassium either alone or in a mixture with lithium as a minor constituent; M 1  is nickel in oxidation state +2; M 2  comprises a metal in oxidation state +4 selected from one or more of manganese, titanium and zirconium; M 3  comprises a metal in oxidation state +2, selected from one or more of magnesium, calcium, copper, zinc and cobalt; M 4  comprises a metal in oxidation state +4, selected from one or more of titanium, manganese and zirconium; M 5  comprises a metal in oxidation state +3, selected from one or more of aluminum, iron, cobalt, molybdenum, chromium, vanadium, scandium and yttrium; wherein 0≦δ≦0.1 V is in the range 0&lt;V&lt;0.5; W is in the range 0&lt;W≦0.5; X is in the range 0≦X&lt;0.5; Y is in the range 0≦Y&lt;0.5; Z is ≧0; and further wherein V+W+X+Y+Z=1. Such materials are useful, for example, as electrode materials in sodium ion battery applications.

FIELD OF THE INVENTION

The present invention relates to novel doped nickelate compounds, theirmethod of preparation, to novel electrodes which utilise an activematerial that comprises said doped nickelate compounds, and to the useof these electrodes, for example in an energy storage device.

BACKGROUND OF THE INVENTION

Sodium-ion batteries are analogous in many ways to the lithium-ionbatteries that are in common use today; they are both reusable secondarybatteries that comprise an anode (negative electrode), a cathode(positive electrode) and an electrolyte material, both are capable ofstoring energy, and they both charge and discharge via a similarreaction mechanism. When a sodium-ion (or lithium-ion battery) ischarging, Na⁺(or Li⁺) ions de-intercalate from the cathode and insertinto the anode. Meanwhile charge balancing electrons pass from thecathode through the external circuit containing the charger and into theanode of the battery. During discharge the same process occurs but inthe opposite direction.

Lithium-ion battery technology has enjoyed a lot of attention in recentyears and provides the preferred portable battery for most electronicdevices in use today; however lithium is not a cheap metal to source andis considered too expensive for use in large scale applications. Bycontrast sodium-ion battery technology is still in its relative infancybut is seen as advantageous; sodium is much more abundant than lithiumand some researchers predict this will provide a cheaper and moredurable way to store energy into the future, particularly for largescale applications such as storing energy on the electrical grid.Nevertheless a lot of work has yet to be done before sodium-ionbatteries are a commercial reality.

NaNi_(0.5)Mn_(0.5)O₂ is a known Na-ion material in which the nickel ispresent as Ni²⁺ while the manganese is present as Mn⁴⁺. The material isordered with the Na and Ni atoms residing in discrete sites within thestructure. The nickel ions (Ni²⁺) are a redox element which contributesto the reversible specific capacity and the manganese ions (Mn⁴⁺) playthe role of a structure stabilizer. Compound NaNi_(0.5)Ti_(0.5)O₂ isanalogous to NaNi_(0.5)Mn_(0.5)O₂ in that the Ni²⁺ ions provide theactive redox centre and the Ti⁴⁺ ions are present for structurestabilization. There is plenty of literature describing the preparationof NaNi_(0.5)Mn_(0.5)O₂ (and to a lesser extent NaNi_(0.5)Ti_(0.5)O₂) asthe precursor for making LiNi_(0.5)Mn_(0.5)O₂ and LiNi_(0.5)Ti_(0.5)O₂by Na→Li ion exchange for Li-ion applications. A direct synthesis methodto make these Li materials may yield undesirable disordered materials,for example, as a result of the lithium and nickel atoms sharingstructural sites. However, recent electrochemical studies reported byKomaba et al Adv. Funct. Mater. 2011, 21, 3859 describe the sodiuminsertion performance of hard-carbon and layered NaNi_(0.5)Mn_(0.5)O₂electrodes in propylene carbonate electrolyte solutions. The resultsobtained show that although NaNi_(0.5)Mn_(0.5)O₂ exhibits somereversible charging and discharging ability, the capacity of thematerial fades by 25% or more, after only 40 cycles.

Work is now being undertaken to find even more efficientelectrochemically active materials, which have large charge capacity,are capable of good cycling performance, highly stable, and of lowtoxicity and high purity. Of course, to be commercially successful, thecathode materials must also be easily and affordably produced. This longlist of requirements is difficult to fulfil but it is understood fromthe literature that the active materials which are most likely tosucceed are those with small particle size and narrow size distribution,with an optimum degree of crystallinity, a high specific surface area,and with uniform morphology.

The present Applicant has also now conducted work which demonstratesthat electrochemical activity is further optimised when the activematerial includes metal constituents with certain defined oxidationstates. Furthermore the Applicant has identified active materials with aspecific crystal structure to be especially active.

The present invention aims to provide novel compounds. Further thepresent invention aims to provide a cost effective electrode thatcontains an active material that is straightforward to manufacture andeasy to handle and store. Another aim of the present invention is toprovide an electrode that has a high initial specific discharge capacityand which is capable of being recharged multiple times withoutsignificant loss in charge capacity.

Therefore, the first aspect of the present invention provides compoundsof the formula:A_(1-δ)M¹ _(V)M² _(W)M³ _(X)M⁴ _(Y)M⁵ _(Z)O₂

-   -   wherein    -   A is one or more alkali metals comprising sodium and/or        potassium, either alone or in a mixture with lithium as a minor        constituent;    -   M¹ is nickel in oxidation state +2    -   M² comprises a metal in oxidation state +4 selected from one or        more of manganese, titanium and zirconium;    -   M³ comprises a metal in oxidation state +2, selected from one or        more of magnesium, calcium, copper, zinc and cobalt;    -   M⁴ comprises a metal in oxidation state +4, selected from one or        more of titanium, manganese and zirconium;    -   M⁵ comprises a metal in oxidation state +3, selected from one or        more of aluminium, iron, cobalt, molybdenum, chromium, vanadium,        scandium and yttrium;    -   wherein    -   0≦δ≦0.1    -   V is in the range 0<V<0.5;    -   W is in the range 0<W≦0.5;    -   X is in the range 0≦X<0.5;    -   Y is in the range 0≦Y<0.5;    -   Z is ≧0;    -   and further wherein V+W+X+Y+Z=1.

Preferably the present invention provides a compound of the aboveformula wherein V is in the range 0.1≦V≦0.45; w is in the range 0<W≦0.5;x is in the range 0≦X<0.5; Y is in the range 0≦Y<0.5; Z is ≧0; andwherein V+W+X+Y+Z=1.

Further preferably the present invention provides a compound of theabove formula wherein V is in the range 0.3≦V 0.45; W is in the range0.1≦W≦0.5; X is in the range 0.05≦X<0.45; Y is in the range 0≦Y≦0.45; Zis ≧0; and wherein V+W+X+Y+Z=1.

In particularly preferred compounds of the above formula, V is in therange 0.3≦V<0.45; W is in the range 0<W≦0.5; X is in the range 0≦X≦0.3;Y is in the range 0≦Y≦0.4; and Z is in the range 0≦Z≦0.5.

Compounds of the above formula in which δ=0.05, are highly beneficial.

In additionally preferred compounds of the present invention M²≠M⁴.

It is particularly advantageous if V+W+Y<0.9 in the compounds of thepresent invention.

The present Applicant has found that not only are the oxidation statesof the metal constituents in the compounds of the present invention acritical feature to the production of highly electrochemically activecompounds but they have also confirmed that having metal constituentswith these particular oxidation states will determine the overallcrystalline structure of the compound. It is known that that there areseveral possible layered structural forms which alkalimetal/metal/oxides may adopt, including O3, P3 and P2. The Applicant hasshown that the oxidation states for the metal constituents cause aparticular structure to be adopted and in particular has determined thatalkali metal/metal/oxide compounds with a metal in +4 oxidation stateand with a sodium content close to 1, will adopt an O3 crystallinestructure. Moreover, the Applicant has demonstrated that alkalimetal/metal/oxides with the metal in oxidation state +4 and with an O3crystalline structure exhibit a much higher electrochemical activitythan similar compounds that do not contain a metal in +4 oxidationstate. The Applicant has also observed that the materials without ametal in +4 oxidation state, typically have a P2 crystalline structure,thus there appears to be a very strong correlation between crystallinestructure, oxidation state and electrochemical activity.

Hence, the present invention provides preferred compounds of theformula:A_(1-δ)M¹ _(V)M² _(W)M³ _(X)M⁴ _(Y)M⁵ _(Z)O₂in an O3 layered structural formwherein

-   -   A is one or more alkali metals comprising sodium and/or        potassium either alone or in a mixture with lithium as a minor        constituent;    -   M¹ is nickel    -   M² comprises a metal selected from one or more of manganese,        titanium and zirconium;    -   M³ comprises a metal selected from one or more of magnesium,        calcium, copper, zinc and cobalt;    -   M⁴ comprises a metal selected from one or more of titanium,        manganese and zirconium;    -   M⁵ comprises a metal selected from one or more of aluminium,        iron, cobalt, molybdenum, chromium, vanadium, scandium and        yttrium.

Especially preferred compounds of the present invention include:

-   NaNi_(0.5−x/2)Ti_(0.5−x/2)Al_(x)O₂;-   NaNi_(0.5−x/2)Mn_(0.5−x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Mg_(x)Ti_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Mg_(x/2)Ti_(x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Ca_(x)Ti_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Co_(x)Ti_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Cu_(x)Ti_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Zn_(x)Ti_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Mg_(x)Zr_(x)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Ca_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.5)Ca_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−Y)Ca_(x)Ti_(Y)O₂;-   NaNi_(0.5−x)Ti_(0.5−x)Mg_(x)Mn_(x)O₂;-   NaNi_(0.5−x)Ti_(0.5−x)Ca_(x)Mn_(x)O₂;-   NaNi_(0.5−x)Ti_(0.5−x)Cu_(x)Mn_(x)O₂;-   NaNi_(0.5−x)Ti_(0.5−x)Co_(x)Mn_(x)O₂;-   NaNi_(0.5−x)Ti_(0.5−x)Zn_(x)Mn_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5)Mg_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5)Ca_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5)Cu_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5)Co_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5)Zn_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Mg_(x)Ti_(y)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Ca_(x)Ti_(y)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Cu_(x)Ti_(y)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Co_(x)Ti_(y)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Zn_(x)Ti_(y)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Mn_(0.25−x/2)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Ca_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Cu_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Co_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Zn_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Mg_(X/2)Ti_(x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Ca_(x/2)Ti_(x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Cu_(x/2)Ti_(x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Co_(x/2)Ti_(x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Zn_(x/2)Ti_(x/2)Al_(x)O₂; and-   Na_(0.95)Ni_(0.3167)Ti_(0.3167)Mg_(0.1583)Mn_(0.2083)O₂

Further, extremely preferred compounds of the present invention include:

-   NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂;-   NaNi_(0.45)Mn_(0.45)Ca_(0.05)Ti_(0.05)O₂;-   NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.05)O₂;-   NaNi_(0.45)Mn_(0.45)Zn_(0.05)Ti_(0.05)O₂ and-   Na_(0.95)Ni_(0.3167)Ti_(0.3167)Mg_(0.1583)Mn_(0.2083)O₂

In a second aspect, the present invention provides an electrodecomprising an active compound of the formula:A_(1-δ)M¹ _(V)M² _(W)M³ _(X)M⁴ _(Y)M⁵ _(Z)O₂

-   -   wherein    -   A is one or more alkali metals comprising sodium and/or        potassium either alone or in a mixture with lithium as a minor        constituent;    -   M¹ is nickel in oxidation state +2    -   M² comprises a metal in oxidation state +4 selected from one or        more of manganese, titanium and zirconium;    -   M³ comprises a metal in oxidation state +2, selected from one or        more of magnesium, calcium, copper, zinc and cobalt;    -   M⁴ comprises a metal in oxidation state +4, selected from one or        more of titanium, manganese and zirconium;    -   M⁵ comprises a metal in oxidation state +3, selected from one or        more of aluminium, iron, cobalt, molybdenum, chromium, vanadium,        scandium and yttrium;    -   wherein    -   0≦δ≦0.1    -   V is in the range 0<V<0.5;    -   W is in the range 0<W≦0.5;    -   X is in the range 0≦X<0.5;    -   Y is in the range 0≦Y<0.5;    -   Z is ≧0;    -   and further wherein V+W+X+Y+Z=1.

Preferably the electrode of the present invention comprises an activecompound of the above formula, wherein V is in the range 0.1≦V≦0.45; wis in the range 0<W≦0.5; x is in the range 0≦X<0.5; Y is in the range0≦Y<0.5; Z is ≧0; and wherein V+W+X+Y+Z=1.

Further preferably the electrode of the present invention comprises anactive compound of the above formula, wherein V is in the range0.3≦V≦0.45; W is in the range 0.1≦W≦0.5; X is in the range 0.05≦X<0.45;Y is in the range 0≦Y≦0.45; Z is ≧0; and wherein V+W+X+Y+Z=1.

Particularly preferred electrodes of the present invention comprise anactive compound of the above formula, wherein V is in the range0.3≦V<0.45; W is in the range 0<W≦0.5; X is in the range 0≦X≦0.3; Y isin the range 0≦Y≦0.4; and Z is in the range 0≦Z≦0.5.

The Applicant has observed that if NiO is present as an impurity phasein samples of the active compounds, then this has a detrimental effecton the electrochemical performance. NiO may be formed during the processof charging the electrode; at this time Ni2+ can be oxidized, using upenergy that would normally be used to charge the active material. Thisis not only an irreversible reaction, but also has a detrimental effecton the cycling performance, resulting in a drop in capacity uponelectrochemical cycling. The formation of NiO by this route is found tobe minimised by reducing the amount of alkali metal in the activecompound and is the purpose for compounds of the invention which haveless than 1 unit of alkali metal. However, it is important to maintainsufficient alkali metal in the compound to ensure that it adopts afavourable crystalline structure such as an O3 type structure.

Electrodes comprising active compounds of the above formula in whichδ=0.05, are highly beneficial.

Additionally preferred electrodes of the present invention comprise anactive compound as described above wherein M²≠M⁴.

Further preferred electrodes of the present invention comprise compoundsof the formula:A_(1-δ)M¹ _(V)M² _(W)M³ _(X)M⁴ _(Y)M⁵ _(Z)O₂in an O3 layered structural formwherein

-   -   A is one or more alkali metals comprising sodium and/or        potassium either alone or in a mixture with lithium as a minor        constituent;    -   M¹ is nickel    -   M² comprises a metal selected from one or more of manganese,        titanium and zirconium;    -   M³ comprises a metal selected from one or more of magnesium,        calcium, copper, zinc and cobalt;    -   M⁴ comprises a metal selected from one or more of titanium,        manganese and zirconium;    -   M⁵ comprises a metal selected from one or more of aluminium,        iron, cobalt, molybdenum, chromium, vanadium, scandium and        yttrium.

Especially preferred electrodes of the present invention comprise activecompounds selected from one or more of:

-   NaNi_(0.5−x/2)Ti_(0.5−x/2)Al_(x)O₂;-   NaNi_(0.5−x/2)Mn_(0.5−x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Mg_(x)Ti_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Mg_(x/2)Ti_(x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Ca_(x)Ti_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Co_(x)Ti_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Cu_(x)Ti_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Mn_(x)Ti_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Mg_(x)Zr_(x)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Ca_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.5)Ca_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Ca_(x)Ti_(Y)O₂;-   NaNi_(0.5−x)Ti_(0.5−x)Mg_(x)Mn_(x)O₂;-   NaNi_(0.5−x)Ti_(0.5−x)Ca_(x)Mn_(x)O₂;-   NaNi_(0.5−x)Ti_(0.5−x)Cu_(x)Mn_(x)O₂;-   NaNi_(0.5−x)Ti_(0.5−x)Co_(x)Mn_(x)O₂;-   NaNi_(0.5−x)Ti_(0.5−x)Zn_(x)Mn_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5)Mg_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5)Ca_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5)Cu_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5)CO_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5)Zn_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Mg_(x)Ti_(y)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Ca_(x)Ti_(y)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Cu_(x)Ti_(y)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Co_(x)Ti_(y)O₂;-   NaNi_(0.5−x)Mn_(0.5−y)Zn_(x)Ti_(y)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Mg_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Ca_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Cu_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Co_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.25−x/2)Zn_(x)Ti_(0.25+x/2)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Mg_(x/2)Ti_(x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Ca_(x/2)Ti_(x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Cu_(x/2)Ti_(x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Co_(x/2)Ti_(x/2)Al_(x)O₂;-   NaNi_(0.5−x)Mn_(0.5−x)Zn_(x/2)Ti_(x/2)Al_(x)O₂; and-   Na_(0.95)Ni_(0.3167)Ti_(0.3167)Mg_(0.1583)Mn_(0.2083)O₂.

Extremely preferred electrodes comprise active compounds selected fromone or more of:

-   NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂;-   NaNi_(0.45)Mn_(0.45)Ca_(0.05)Ti_(0.05)O₂;-   NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.05)O₂;-   NaNi_(0.45)Mn_(0.45)Zn_(0.05)Ti_(0.05)O₂, and-   Na_(0.95)Ni_(0.3167)Ti_(0.3167)Mg_(0.1583)Mn_(0.2083)O₂.

The electrodes according to the present invention are suitable for usein many different applications, for example energy storage devices,rechargeable batteries, electrochemical devices and electrochromicdevices.

Advantageously, the electrodes according to the invention are used inconjunction with a counter electrode and one or more electrolytematerials. The electrolyte materials may be any conventional or knownmaterials and may comprise either aqueous electrolyte(s) or non-aqueouselectrolyte(s) or mixtures thereof.

In a third aspect, the present invention provides an energy storagedevice that utilises an electrode comprising the active materialsdescribed above, and particularly an energy storage device for use asone or more of the following: a sodium and/or potassium ion cell; asodium and/or potassium metal cell; a non-aqueous electrolyte sodiumand/or potassium ion; an aqueous electrolyte sodium and/or potassium ioncell. In each case lithium may also be present as a minor constituent.

The novel compounds of the present invention may be prepared using anyknown and/or convenient method. For example, the precursor materials maybe heated in a furnace so as to facilitate a solid state reactionprocess.

A fourth aspect of the present invention provides a particularlyadvantageous method for the preparation of the compounds described abovecomprising the steps of:

a) mixing the starting materials together, preferably intimately mixingthe starting materials together and further preferably pressing themixed starting materials into a pellet;

b) heating the mixed starting materials in a furnace at a temperature ofbetween 400° C. and 1500° C., preferably a temperature of between 500°C. and 1200° C., for between 2 and 20 hours; and

c) allowing the reaction product to cool.

Preferably the reaction is conducted under an atmosphere of ambient air,and alternatively under an inert gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to thefollowing figures in which:

FIG. 1(A) shows the third Cycle Discharge Voltage Profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for prior artcathode material, NaNi_(0.5)Mn_(0.5)O₂, prepared according to Example 1;

FIG. 1(B) shows the third Cycle Discharge Voltage Profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for cathodematerial NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂ according to thepresent invention and prepared according to Example 2;

FIG. 1(C) shows the third Cycle Discharge Voltage Profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for cathodematerial NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂ according to thepresent invention and prepared according to Example 3;

FIG. 1(D) shows the third Cycle Discharge Voltage Profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for cathodematerial NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂ according to thepresent invention and prepared according to Example 4;

FIG. 1(E) shows the third Cycle Discharge Voltage Profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for cathodematerial NaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂ according to thepresent invention and prepared according to Example 5;

FIG. 2(A) shows the third Cycle Differential Capacity Profiles(Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) forprior art cathode material NaNi_(0.5)Mn_(0.5)O₂, prepared according toExample 1;

FIG. 2(B) shows the third Cycle Differential Capacity Profiles(Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) forcathode material NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂ according tothe present invention and prepared according to Example 2;

FIG. 2(C) shows the third Cycle Differential Capacity Profiles(Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) forcathode material NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂ according tothe present invention and prepared according to Example 3;

FIG. 2(D) shows the third Cycle Differential Capacity Profiles(Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) forcathode material NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂ according tothe present invention and prepared according to Example 4;

FIG. 2(E) shows the third Cycle Differential Capacity Profiles(Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) forcathode material NaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂ according tothe present invention and prepared according to Example 5;

FIG. 3(A) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for prior art cathode material NaNi_(0.5)Mn_(0.5)O₂, preparedaccording to Example 1;

FIG. 3(B) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for cathode material NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂,according to the present invention and prepared according to Example 2;

FIG. 3(C) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for cathode material NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂,according to the present invention and prepared according to Example 3;

FIG. 3(D) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for cathode material NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂,according to the present invention and prepared according to Example 4;

FIG. 3(E) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for cathode material NaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂,according to the present invention and prepared according to Example 5;

FIG. 4 shows Cycle Life (Cathode Specific Capacity [mAh/g] versus CycleNumber) for a Hard Carbon//NaNi_(0.45)Mg_(0.45)Mg_(0.05)Ti_(0.05)O₂Cell;

FIG. 5(A) shows Third Cycle Discharge Voltage Profiles (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for prior artcathode material NaNi_(0.5)Ti_(0.5)O₂, made according to Example 6;

FIG. 5(B) shows Third Cycle Discharge Voltage Profiles (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for cathodematerial, NaNi_(0.40)Ti_(0.50)Mg_(0.10)O₂, according to the presentinvention and made according to Example 7;

FIG. 5(C) shows Third Cycle Discharge Voltage Profiles (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for prior artcathode material NaNi_(0.40)Ti_(0.40)Mg_(0.10)Mn_(0.10)O₂ according tothe present invention and made according to Example 8;

FIG. 6(A) shows Third Cycle Differential Capacity Profiles (DifferentialCapacity [mAh/g/V] Na-ion Cell Voltage [V]) for prior art cathodematerial NaNi_(0.5)Ti_(0.5)O₂, prepared according to Example 6;

FIG. 6(B) shows Third Cycle Differential Capacity Profiles (DifferentialCapacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for cathode materialNaNi_(0.40)Ti_(0.50)Mg_(0.10)O₂, according to the present invention andprepared according to Example 7;

FIG. 6(C) shows Third Cycle Differential Capacity Profiles (DifferentialCapacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for cathode materialaccording NaNi_(0.40)Ti_(0.40)Mg_(0.10)Mn_(0.10)O₂, to the presentinvention and prepared according to Example 8;

FIG. 7(A) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for prior art cathode material NaNi_(0.5)Ti_(0.5)O₂, preparedaccording to Example 6;

FIG. 7(B) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for cathode material NaNi_(0.40)Ti_(0.50)Mg_(0.10)O₂, preparedaccording to Example 7;

FIG. 7(C) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for cathode material NaNi_(0.40)Ti_(0.40)Mg_(0.10)Mn_(0.10)O₂,prepared according to Example 8;

FIG. 8(A) shows Third Cycle Discharge Voltage Profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for a HardCarbon//NaNi_(0.40)Mn_(0.4)Mg_(0.05)Ti_(0.05)Al_(0.1)O₂ Cell;

FIG. 8(B) shows Third Cycle Differential Capacity Profiles (DifferentialCapacity [mAh/g/V] Na-ion Cell Voltage [V]) for a HardCarbon//NaNi_(0.40)Mn_(0.4)Mg_(0.05)Ti_(0.05)Al_(0.1)O₂ Cell;

FIG. 8(C) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for a HardCarbon//NaNi_(0.40)Mn_(0.40)Mn_(0.4)Mg_(0.05)Ti_(0.05)Al_(0.1)O₂ Cell;

FIG. 9(A) shows Third Cycle Discharge Voltage Profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for a HardCarbon//NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.05)O₂ Cell;

FIG. 9(B) shows Third Cycle Differential Capacity Profiles (DifferentialCapacity [mAh/gN] versus Na-ion Cell Voltage [V]) for a HardCarbon//NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.05)O₂ Cell;

FIG. 9(C) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for a Hard Carbon//NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.0.5)O₂Cell;

FIG. 10(A) shows Third Cycle Discharge Voltage Profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for a HardCarbon//NaNi_(0.40)Mn_(0.40)Ca_(0.10)Ti_(0.10)O₂ Cell;

FIG. 10(B) shows Third Cycle Differential Capacity Profiles(Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for aHard Carbon//NaNi_(0.40)Mn_(0.40)Ca_(0.10)Ti_(0.10)O₂ Cell;

FIG. 10(C) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for a Hard Carbon//NaNi_(0.40)Mn_(0.40)Ca_(0.10)Ti_(0.10)O₂Cell;

FIG. 11(A) shows Third Cycle Discharge Voltage Profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for a HardCarbon//NaNi_(0.40)Mn_(0.40)Zn_(0.10)Ti_(0.10)O₂ Cell;

FIG. 11(B) shows Third Cycle Differential Capacity Profiles(Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for aHard Carbon//NaNi_(0.40)Mn_(0.40)Zn_(0.10)Ti_(0.10)O₂ Cell;

FIG. 11(C) shows Charge-Discharge Voltage Profiles for first 4 cycles(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for a Hard Carbon//NaNi_(0.40)Mn_(0.40)Zn_(0.10)Ti_(0.10)O₂Cell;

FIG. 12(A) is an XRD of NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂according to the present invention and prepared according to Example 2;

FIG. 12(B) is an XRD of NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂according to the present invention and prepared according to Example 3;

FIG. 12(C) is an XRD of NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂according to the present invention and prepared according to Example 4;

FIG. 12(D) is an XRD of NaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂according to the present invention and prepared according to Example 5;

FIG. 12(E) is an XRD of NaNi_(0.40)Mn_(0.4)Mg_(0.05)Ti_(0.05)Al_(0.1)O₂prepared according to Example 9;

FIG. 12(F) is an XRD of NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.0.5)O₂,prepared according to Example 10;

FIG. 12(G) is an XRD of NaNi_(0.40)Mn_(0.40)Zn_(0.10)Ti_(0.10)O₂,prepared according to Example 12;

FIG. 13(A) is an XRD of Na_(0.7)MnO_(2.05), prepared according tocomparative Example 13.

FIG. 13(B) shows the constant current cycling data (Na-ion Cell Voltage[V] versus Cumulative Cathode Specific Capacity [mAh/g]) for the first 4cycles of the comparative material Na_(0.7)MnO_(2.05) (X1386) activecathode material (P2 structure) in a Na-ion cell where it is coupledwith a capacity balanced Hard Carbon (Carbotron P/J) anode material.

FIG. 14(A) is an XRD ofNa_(0.95)Ni_(0.3167)Ti_(0.3167)Mg_(0.1583)Mn_(0.2083)O₂ preparedaccording to Example 14.

FIG. 14(B) shows the constant current cycling data (Na-ion Cell Voltage[V] versus Cumulative Cathode Specific Capacity [mAh/g]) for the first 4cycles of the Na_(0.95)Ni_(0.3167)Mn_(0.3167)Mg_(0.1583)Ti_(0.2083)O₂(X1380) active material in a Na-ion cell where it is coupled with acapacity balanced Hard Carbon (Carbotron P/J) anode material.

DETAILED DESCRIPTION

The materials according to the present invention are prepared using thefollowing generic method:

Generic Synthesis Method:

Stoichiometric amounts of the precursor materials are intimately mixedtogether and pressed into a pellet. The resulting mixture is then heatedin a tube furnace or a chamber furnace using either an ambient airatmosphere, or a flowing inert atmosphere (e.g. argon or nitrogen), at afurnace temperature of between 400° C. and 1500° C. until reactionproduct forms; for some materials a single heating step is used and forothers (as indicated below in Table 1) more than one heating step isused. When cool, the reaction product is removed from the furnace andground into a powder.

Using the above method, active materials were prepared, Examples 1 to14, as summarised below in Table 1:

TABLE 1 STARTING EXAMPLE TARGET COMPOUND MATERIALS FURNACE CONDITIONS 1NaNi_(0.5)Mn_(0.5)O₂ Na₂CO_(3,) 1) Air/700° C., dwell time of 8 hours.Prior art NiCO_(3.) 2) Air/900° C., dwell time of 8 hours. MnO₂ 2NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂ Na₂CO₃ 1) Air/800° C., dwelltime of 8 hours. NiCO₃ 2) Air/900° C., dwell time of 8 hours. Mg(OH)₂MnO₂ TiO₂ 3 NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂ Na₂CO₃ 1) Air/800°C., dwell time of 8 hours. NiCO₃ 2) Air/900° C., dwell time of 8 hours.Mg(OH)₂ MnO₂ TiO₂ 4 NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂ Na₂CO₃ 1)Air/900° C., dwell time of 8 hours. NiCO₃ 2) Air/900° C., dwell time of8 hours. MnO₂ Mg(OH)₂ TiO₂ 5 NaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂Na₂CO₃ 1) Air/900° C., dwell time of 8 hours NiCO₃ 2) Air/900° C., dwelltime of 8 hours. MnO₂ Mg(OH)₂ TiO₂ 6 NaNi_(0.5)Ti_(0.5)O₂ Na₂CO₃ 1)Air/900° C., dwell time of 8 hours Prior art NiCO₃ 2) Air/900° C., dwelltime of 8 hours. TiO₂ 7 NaNi_(0.40)Ti_(0.50)Mg_(0.10)O₂ Na₂CO₂1)Air/900° C., dwell time of 8 hours NiCO_(3,) 2)/900° C., dwell time of8 hours. TiO_(2,) Mg(OH)₂ 8 NaNi_(0.40)Ti_(0.40)Mg_(0.10)Mn_(0.10)O₂Na₂CO_(3,) 1)Air/900° C., dwell time of 8 hours NiCO_(3,) 2) Air/900°C., dwell time of 8 hours. TiO_(2,) Mg(OH)_(2,) MnO₂ 9NaNi_(0.40)Mn_(0.40)Mg_(0.05)Ti_(0.05)Al_(0.1)O₂ Na₂CO₃ 1)Air/800° C.,dwell time of 8 hours NiCO₃ 2) Air/900° C., dwell time of 8 hours.Mg(OH)₂ MnO₂ TiO₂ Al(OH)₃ 10 NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.05)O₂Na₂CO_(3,) 1)Air/900° C., dwell time of 8 hours NiCO_(3,) 2) Air/900°C., dwell time of 8 hours. MnO₂ CuO TiO₂ 11NaNi_(0.40)Mn_(0.40)Ca_(0.10)Ti_(0.10)O₂ Na₂CO_(3,) 1)Air/900° C., dwelltime of 8 hours NiCO_(3,) 2) Air/900° C., dwell time of 8 hours. MnO₂ 3)Air/950° C., dwell time of 8 hours. CaCO₃ TiO₂ 12NaNi_(0.40)Mn_(0.40)Zn_(0.10)Ti_(0.10)O₂ Na₂CO₃ 1)Air/900° C., dwelltime of 8 hours NiCO₃ 2) Air/900° C., dwell time of 8 hours. MnO₂ CuOTiO₂ 13 Na_(0.7)MnO_(2.05) 0.7 Na₂CO₃ Mixing solvent acetone Comparative0.5 Mn₂O₃ 700° C. in air, dwell time of 10 hours 700° C. in air, dwelltime of 10 hours 800° C. in air, dwell time of 20 hours 900° C. in air,dwell time of 8 hours 1000° C. in air, dwell time of 8 hours (samplereground and repelletised between each firing) 14Na_(0.95)Ni_(0.3167)Ti_(0.3167)Mg_(0.1583)Mn_(0.2083)O₂ 0.475 MixingSolvent: Acetone Na₂CO₃ 900° C. in air, dwell time of 8 hours 0.3167NiCO₃ 0.3167 TiO₂ 0.2083 MnO₂ 0.1583 Mg(OH)₂Product Analysis Using XRD

All of the product materials were analysed by X-ray diffractiontechniques using a Siemens D5000 powder diffractometer to confirm thatthe desired target materials had been prepared, to establish the phasepurity of the product material and to determine the types of impuritiespresent. From this information it is possible to determine the unit celllattice parameters.

The operating conditions used to obtain the XRD spectra illustrated inFIGS. 12(A)-12(G), and FIGS. 13(A) and 14(A) are as follows:

Slits sizes: 1 mm, 1 mm, 0.1 mm

Range: 2θ=5°-60°

X-ray Wavelength=1.5418 Å (Angstoms)-(Cu Kα)

Speed: 0.5 seconds/step

Increment: 0.015°

Electrochemical Results

The target materials were tested either i) using a lithium metal anodetest cell, or ii) using a Na-ion test cell using a hard carbon anode. Itis also possible to test using a Li-ion cell with a graphite anode.Cells may be made using the following procedures:

A Na-ion electrochemical test cell containing the active material isconstructed as follows:

Generic Procedure to Make a Hard Carbon Na-Ion Cell

The positive electrode is prepared by solvent-casting a slurry of theactive material, conductive carbon, binder and solvent. The conductivecarbon used is Super P (Timcal). PVdF co-polymer (e.g. Kynar Flex 2801,Elf Atochem Inc.) is used as the binder, and acetone is employed as thesolvent. The slurry is then cast onto glass and a free-standingelectrode film is formed as the solvent evaporates. The electrode isthen dried further at about 80° C. The electrode film contains thefollowing components, expressed in percent by weight: 80% activematerial, 8% Super P carbon, and 12% Kynar 2801 binder. Optionally, analuminium current collector may be used to contact the positiveelectrode.

The negative electrode is prepared by solvent-casting a slurry of thehard carbon active material (Carbotron P/J, supplied by Kureha),conductive carbon, binder and solvent. The conductive carbon used isSuper P (Timcal). PVdF co-polymer (e.g. Kynar Flex 2801, Elf AtochemInc.) is used as the binder, and acetone is employed as the solvent. Theslurry is then cast onto glass and a free-standing electrode film isformed as the solvent evaporates. The electrode is then dried further atabout 80° C. The electrode film contains the following components,expressed in percent by weight: 84% active material, 4% Super P carbon,and 12% Kynar 2801 binder. Optionally, a copper current collector may beused to contact the negative electrode.

Cell Testing

The cells are tested as follows, using Constant Current Cyclingtechniques.

The cell is cycled at a given current density between pre-set voltagelimits. A commercial battery cycler from Maccor Inc. (Tulsa, Okla., USA)is used. On charge, sodium (lithium) ions are extracted from the cathodeactive material. During discharge, sodium (lithium) ions are re-insertedinto the cathode active material.

Results:

Referring to FIGS. 1(A)-1(E).

FIGS. 1(A), 1(B), 1(C), 1(D) and 1(E) show the third cycle dischargevoltage profiles (Na-ion Cell Voltage [V] versus Cathode SpecificCapacity [mAh/g]) for several HardCarbon//NaNi_(0.5−X)(Mn_(0.5−X)Mg_(X)Ti_(X)O₂ cells. The cathodematerials used to make these cells were NaNi_(0.5)Mn_(0.5)O₂ (FIG. 1(A),prior art), NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂ (FIG. 1(B)),NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂ (FIG. 1(C)),NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂ (FIG. 1(D)) andNaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂ (FIG. 1 (E)).

The data shown in FIGS. 1(A), (B), (C), (D) and (E) are derived from theconstant current cycling data for theNaNi_(0.5−X)Mn_(0.5−X)Mg_(X)Ti_(X)O₂ active materials in a Na-ion cellwhere these cathode materials were coupled with a Hard Carbon (CarbotronP/J) anode material. The electrolyte used is a 0.5 M solution of NaClO₄in propylene carbonate. The constant current data were collected at anapproximate current density of 0.10 mA/cm² between voltage limits of1.50 and 4.00 V. To ensure that the Na-ion cells were fully charged,they were potentiostatically held at 4.0 V at the end of the constantcurrent charging process until the current density dropped to 20% of theconstant current value. The testing was carried out at room temperature.During the cell charging process, sodium ions are extracted from thecathode active materials, and inserted into the Hard Carbon anode.During the subsequent discharge process, sodium ions are extracted fromthe Hard Carbon and re-inserted into the cathode active materials.

The third cycle discharge processes for these cells correspond to thefollowing cathode specific capacities: (A) NaNi_(0.5)Mn_(0.5)O₂=88mAh/g; (B) NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.0.5)O₂=77 mAh/g; (C)NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂=86 mAh/g; (D)NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂=116 mAh/g; and (E)NaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂=109 mAh/g.

It should be noted from FIGS. 1(A), (B), (C), (D) and (E) that as thelevels of Mg and Ti increase, there is a smoothing of the dischargevoltage profile. This is an important observation as it is notadvantageous for application purposes to have voltage ‘steps’ in thedischarge voltage profile, thus the materials according to the presentinvention, NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂,NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂,NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂, andNaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂, provide significant advantageover prior art material NaNi_(0.5)Mn_(0.5)O₂.

Referring to FIGS. 2(A)-(E).

FIGS. 2(A)-(E) show the third cycle differential capacity profiles(Differential Capacity [mAh/g/V] Na-ion Cell Voltage [V]) for severalHard Carbon//NaNi_(0.5−X)Mn_(0.5−X)Mg_(X)Ti_(X)O₂ cells. The cathodematerials used to make these cells were: NaNi_(0.5)Mn_(0.5)O₂ (FIG. 2A,prior art), NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.0.5)O₂ (FIG. 2(B)),NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂ (FIG. 2(C)),NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂ (FIG. 2(D)) andNaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂ (FIG. 2(E)).

The data shown in FIGS. 2(A)-(E) are derived from the constant currentcycling data for the NaNi_(0.5−X)Mn_(0.5−X)Mg_(X)Ti_(X)O₂ activematerials in a Na-ion cell where these cathode materials were coupledwith a Hard Carbon (Carbotron P/J) anode material. The electrolyte usedis a 0.5 M solution of NaClO₄ in propylene carbonate. The constantcurrent data were collected at an approximate current density of 0.10mA/cm² between voltage limits of 1.50 and 4.00 V. To ensure that theNa-ion cells were fully charged, they were potentiostatically held at4.0 V at the end of the constant current charging process until thecurrent density dropped to 20% of the constant current value. Thetesting was carried out at room temperature. During the cell chargingprocess, sodium ions are extracted from the cathode active materials,and inserted into the Hard Carbon anode. During the subsequent dischargeprocess, sodium ions are extracted from the Hard Carbon and re-insertedinto the cathode active materials. The data shown in FIGS. 2(A)-(E)characterize the charge-discharge behaviour of the Na-ion cells undertest. Differential capacity data have been demonstrated to allowcharacterization of the reaction reversibility, order-disorderphenomenon and structural phase changes within the ion insertion system.

The differential capacity data for the NaNi_(0.5)Mn_(0.5)O₂ cathode(FIG. 2A) shows a very structured charge-discharge behaviourcharacterized by several sharp differential capacity peaks in both thecharge and discharge processes. Peaks in the differential capacity datacorrespond to plateaux (voltage steps) in the voltage versus capacityprofiles. It should be noted from FIGS. 2(B)-(E) that as the levels ofMg and Ti increase, there is a dramatic change in the differentialcapacity profiles (see for example the difference between the dataderived from the Na-ion cell incorporating the NaNi_(0.5)Mn_(0.5)O₂cathode material (FIG. 2A) and that for the Na-ion cell incorporatingthe NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂ cathode material (FIG.2B)). This is an important observation as it is not advantageous forapplication purposes to have voltage ‘steps’ in the discharge voltageprofile. Increasing levels of Mg and Ti in the cathode materials (FIG.2(C) to FIG. 2(E)) cause a further loss of structure in the differentialcapacity data and reflect directly the smoothing of the voltage profiledue to the Mg and Ti incorporation into the structure of the cathodematerial. These observations demonstrate that the materials according tothe present invention, i.e. NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂(FIG. 2(B)), NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂ (FIG. 2(C)),NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂ (FIG. 2(D)) andNaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂ (FIG. 2(E)), provide furthersignificant advantageous over prior art material NaNi_(0.5)Mn_(0.5)O₂(FIG. 2(A)).

Referring to FIGS. 3(A)-(E).

FIGS. 3(A)-(E) show the first four charge-discharge cycles (Na-ion CellVoltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) forseveral Hard Carbon//NaNi_(0.5-X)Mn_(0.5−X)Mg_(X)Ti_(X)O₂ cells. Thecathode materials used to make these cells were: NaNi_(0.5)Mn_(0.5)O₂(FIG. 3(A), prior art), NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂ (FIG.3(B)), NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂ (FIG. 3(C)),NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂ (FIG. 3(D) andNaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂ (FIG. 3(E)).

The data shown in FIGS. 3(A)-(E) are derived from the constant currentcycling data for the NaNi_(0.5−X)Mn_(0.5−X)Mg_(X)Ti_(X)O₂ activematerials in a Na-ion cell where these cathode materials were coupledwith a Hard Carbon (Carbotron P/J) anode material. The electrolyte usedis a 0.5 M solution of NaClO₄ in propylene carbonate. The constantcurrent data were collected at an approximate current density of 0.10mA/cm² between voltage limits of 1.50 and 4.00 V. To ensure that theNa-ion cells were fully charged, they were potentiostatically held at4.0 V at the end of the constant current charging process until thecurrent density dropped to 20% of the constant current value. Thetesting was carried out at room temperature. During the cell chargingprocess, sodium ions are extracted from the cathode active materials,and inserted into the Hard Carbon anode. During the subsequent dischargeprocess, sodium ions are extracted from the Hard Carbon and re-insertedinto the cathode active materials.

The data in FIGS. 3(A)-(E) indicate the reversibility of the sodium ionextraction-insertion reactions. It is clear from inspection that thevoltage profiles for the cathode iterations incorporating Mg and Ti(i.e. FIGS. 3(B)-(E)) show a less-structured profile. In addition, thelevel of voltage hysteresis (i.e. the voltage difference between thecharge and discharge processes) is extremely small, indicating theexcellent kinetics of the extraction-insertion reactions. This is animportant property that is useful for producing a high rate activematerial, thus materials NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂ (FIG.3(B)), NaNi_(0.40)Mn_(0.40)Mg_(0.10)Ti_(0.10)O₂ (FIG. 3(C)),NaNi_(0.35)Mn_(0.35)Mg_(0.15)Ti_(0.15)O₂ (FIG. 3(D) andNaNi_(0.30)Mn_(0.30)Mg_(0.20)Ti_(0.20)O₂ (FIG. 3(E)) exhibit stillfurther advantages over prior art material NaNi_(0.5)Mn_(0.5)O₂ (FIG.3(A).

Referring to FIG. 4.

FIG. 4 shows the constant current cycling data for theNaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂ active material (preparedaccording to Example 2) in a Na-ion cell where it is coupled with a HardCarbon (Carbotron P/J) anode material. The electrolyte used is a 0.5 Msolution of NaClO₄ in propylene carbonate. The constant current datawere collected at an approximate current density of 0.10 mA/cm² betweenvoltage limits of 1.50 and 4.00 V. To ensure that the Na-ion cell wasfully charged, the cell was potentiostatically held at 4.00 V at the endof the constant current charging process until the current densitydropped to 20% of the constant current value. The testing was carriedout at room temperature. It is evident that sodium ions are extractedfrom the cathode active material,NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂, and inserted into the HardCarbon anode during the initial charging of the cell. During thesubsequent discharge process, sodium ions are extracted from the HardCarbon and re-inserted into the NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂cathode active material. The first discharge process corresponds to aspecific capacity for the cathode of about 87 mAh/g, indicating thereversibility of the sodium ion extraction-insertion processes.

Na-ion cells reported in the literature commonly show relatively rapidcapacity fade on cycling. It is common for these cells to fade incapacity by more than 50% in the first 30 cycles. The data shown in FIG.4, show that the Hard Carbon//NaNi_(0.45)Mn_(0.45)Mg_(0.05)Ti_(0.05)O₂cell demonstrates quite exceptional cycling behaviour. There is almostno capacity fade over the first 100 cycles. The initial specificcapacity for the cathode is about 87 mAh/g and after 100 cycles thespecific capacity for the cathode is about 85 mAh/g, indicating acapacity fade of less than 3%.

Referring to FIGS. 5(A)-(C).

FIGS. 5(A)-(C) show the third cycle discharge voltage profiles (Na-ionCell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for severalHard Carbon//NaNi_(V)Mn_(W)Mg_(X)Ti_(Y)O₂ cells. The cathode materialsused to make these cells were: NaNi_(0.5)Ti_(0.5)O₂ (FIG. 5A)),NaNi_(0.40)Ti_(0.50)Mg_(0.10)O₂ (FIG. 5(B)), andNaNi_(0.40)Ti_(0.40)Mg_(0.00)Mn_(0.10)O₂ (FIG. 5(C)).

The data shown in FIGS. 5(A)-(C) are derived from the constant currentcycling data for the NaNi_(V)Mn_(W)Mg_(X)Ti_(Y)O₂ active materials in aNa-ion cell where these cathode materials were coupled with a HardCarbon (Carbotron P/J) anode material. The electrolyte used is a 0.5 Msolution of NaClO₄ in propylene carbonate. The constant current datawere collected at an approximate current density of 0.10 mA/cm² betweenvoltage limits of 1.50 and 4.00 V. To ensure that the Na-ion cells werefully charged, the cells were potentiostatically held at 4.0 V at theend of the constant current charging process until the current densitydropped to 20% of the constant current value. The testing was carriedout at room temperature. During the cell charging process, sodium ionsare extracted from the cathode active materials, and inserted into theHard Carbon anode. During the subsequent discharge process, sodium ionsare extracted from the Hard Carbon and re-inserted into the cathodeactive materials. From inspection of FIGS. 5(A)-(C) we can detect thatwith the incorporation of Mg and Mn in the cathode active material thereis a dramatic increase in the reversible cathode specific capacity. Thethird cycle discharge processes for these cells correspond to thefollowing cathode specific capacities: NaNi_(0.5)Ti_(0.5)O₂=79 mAh/g(FIG. 5(A)); NaNi_(0.40)Ti_(0.50)Mg_(0.10)O₂=103 mAh/g (FIG. 5(B); andNaNi_(0.40)Ti_(0.40)Mg_(0.10)Mn_(0.10)O₂=125 mAh/g (FIG. 5(C).

Referring to FIGS. 6(A)-(C).

FIGS. 6(A)-(C) show the third cycle differential capacity profiles(Differential Capacity [mAh/g/V] Na-ion Cell Voltage [V]) for severalHard Carbon//NaNi_(V)Mn_(W)Mg_(X)Ti_(Y)O₂ cells. The cathode materialsused to make these cells were: NaNi_(0.5)Ti_(0.5)O₂ (FIG. 6(A)),NaNi_(0.40)Ti_(0.50)Mg_(0.10)O₂ (FIG. 6(B)), andNaNi_(0.40)Ti_(0.40)Mg_(0.10)Mn_(0.10)O₂ (FIG. 6(C)).

The data shown in FIGS. 6(A)-(C) are derived from the constant currentcycling data for the NaNi_(V)Mn_(W)Mg_(X)Ti_(Y)O₂ active materials in aNa-ion cell where these cathode materials were coupled with a HardCarbon (Carbotron P/J) anode material. The electrolyte used is a 0.5 Msolution of NaClO₄ in propylene carbonate. The constant current datawere collected at an approximate current density of 0.10 mA/cm² betweenvoltage limits of 1.50 and 4.00 V. To ensure that the Na-ion cells werefully charged, the cells were potentiostatically held at 4.0 V at theend of the constant current charging process until the current densitydropped to 20% of the constant current value. The testing was carriedout at room temperature. During the cell charging process, sodium ionsare extracted from the cathode active materials, and inserted into theHard Carbon anode. During the subsequent discharge process, sodium ionsare extracted from the Hard Carbon and re-inserted into the cathodeactive materials. The data shown in FIGS. 6(A)-(C) characterize thecharge-discharge behaviour of the Na-ion cells under test. Differentialcapacity data have been demonstrated to allow characterization of thereaction reversibility, order-disorder phenomenon and structural phasechanges within the ion insertion system.

The differential capacity data for the NaNi_(0.5)Ti_(0.5)O₂ cathode(FIG. 6A) show a structured charge-discharge behaviour characterized bya sharp differential capacity peak at about 2.85 V on discharge. Peaksin the differential capacity data correspond to plateaux (voltage steps)in the voltage versus capacity profiles.

It should be noted from FIGS. 6(B)-(C) that on incorporation of Mg andMn into the cathode material, there is a dramatic change in thedifferential capacity profiles (see for example the difference betweenthe data derived from the Na-ion cell incorporating theNaNi_(0.5)Ti_(0.5)O₂ cathode material (FIG. 6(A)) and that for theNa-ion cell incorporating the NaNi_(0.40)Ti_(0.40)Mg_(0.10)Mn_(0.10)O₂cathode material (FIG. 6(C)). This is an important observation because,as described above, it is not advantageous for application purposes tohave voltage ‘steps’ in the discharge voltage profile.

Referring to FIGS. 7(A)-(C).

FIGS. 7(A)-(C) show the first four charge-discharge cycles (Na-ion CellVoltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) forseveral Hard Carbon//NaNi_(V)Mn_(W)Mg_(X)Ti_(Y)O₂ cells. The cathodematerials used to make these cells were: NaNi_(0.5)Ti_(0.5)O₂ (FIG.7(A)), NaNi_(0.40)Ti_(0.50)Mg_(0.10)O₂ (FIG. 7(B)), andNaNi_(0.40)Ti_(0.40)Mg_(0.10)Mn_(0.10)O₂ (FIG. 7(C)).

The data shown in FIGS. 7(A)-(C) are derived from the constant currentcycling data for the NaNi_(V)Mn_(W)Mg_(X)Ti_(Y)O₂ active materials in aNa-ion cell where these cathode materials were coupled with a HardCarbon (Carbotron P/J) anode material. The electrolyte used is a 0.5 Msolution of NaClO₄ in propylene carbonate. The constant current datawere collected at an approximate current density of 0.10 mA/cm² betweenvoltage limits of 1.50 and 4.00 V. To ensure that the Na-ion cells werefully charged, the cells were potentiostatically held at 4.0 V at theend of the constant current charging process until the current densitydropped to 20% of the constant current value. The testing was carriedout at room temperature. During the cell charging process, sodium ionsare extracted from the cathode active materials, and inserted into theHard Carbon anode. During the subsequent discharge process, sodium ionsare extracted from the Hard Carbon and re-inserted into the cathodeactive materials. The data in FIGS. 7(A)-(C) indicate the reversibilityof the sodium ion extraction-insertion reactions. It is clear frominspection that the voltage profiles for the cathode iterationsincorporating Mg and Mn (i.e. FIGS. 7(B) and 7(C)) show aless-structured profile. In addition, the level of voltage hysteresis(i.e. the voltage difference between the charge and discharge processes)is extremely small, indicating the excellent kinetics of theextraction-insertion reactions. This is an important property that isuseful for producing a high rate active material. Thus the compounds ofthe present invention, NaNi_(0.40)Ti_(0.50)Mg_(0.10)O₂ (FIG. 7(B)), andNaNi_(0.40)Ti_(0.40)Mg_(0.10)Mn_(0.10)O₂ (FIG. 7(C)) demonstratesignificant advantages over prior art material NaNi_(0.5)Ti_(0.5)O₂(FIG. 7(A)).

Referring to FIGS. 8(A)-(C).

The data shown in FIGS. 8(A)-(C) are derived from the constant currentcycling data for a NaNi_(0.40)Mn_(0.40)Mg_(0.05)Ti_(0.05)Al_(0.1)O₂active material in a Na-ion cell where this cathode material was coupledwith a Hard Carbon (Carbotron P/J) anode material. The electrolyte usedis a 0.5 M solution of NaClO₄ in propylene carbonate. The constantcurrent data were collected at an approximate current density of 0.10mA/cm² between voltage limits of 1.50 and 4.00 V. To fully charge thecell, the Na-ion cell was potentiostatically held at 4.0 V at the end ofthe constant current charging process until the current density droppedto 20% of the constant current value. The testing was carried out atroom temperature. During the cell charging process, sodium ions areextracted from the cathode active material, and inserted into the HardCarbon anode. During the subsequent discharge process, sodium ions areextracted from the Hard Carbon and re-inserted into the cathode activematerial.

FIG. 8(A) shows the third cycle discharge voltage profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for the HardCarbon//NaNi_(0.40)Mn_(0.40)Mg_(0.05)Ti_(0.05)Al_(0.1)O₂ cell. Thecathode specific capacity corresponds to 73 mAh/g.

FIG. 8(B) shows the third cycle differential capacity profiles(Differential Capacity [mAh/g/V] Na-ion Cell Voltage [V]) for the HardCarbon//NaNi_(0.40)Mn_(0.40)Mg_(0.05)Ti_(0.05)Al_(0.1)O₂ cell. Thesesymmetrical data demonstrate the excellent reversibility of the ionextraction-insertion reactions in this Na-ion cell.

FIG. 8(C) shows the first four charge-discharge cycles (Na-ion CellVoltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for theHard Carbon//NaNi_(0.40)Mn_(0.40)Mg_(0.05)Ti_(0.05)Al_(0.1)O₂ cell.These data demonstrate that the level of voltage hysteresis (i.e. thevoltage difference between the charge and discharge processes) isextremely small, indicating the excellent kinetics of theextraction-insertion reactions.

Referring to FIGS. 9(A)-(C).

The data shown in FIGS. 9(A)-(C) are derived from the constant currentcycling data for a NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.05)O₂ activematerial in a Na-ion cell where this cathode material was coupled with aHard Carbon (Carbotron P/J) anode material. The electrolyte used is a0.5 M solution of NaClO₄ in propylene carbonate. The constant currentdata were collected at an approximate current density of 0.10 mA/cm²between voltage limits of 1.50 and 4.00 V. To ensure that the Na-ioncell was fully charged, the cell was potentiostatically held at 4.0 V atthe end of the constant current charging process until the currentdensity dropped to 20% of the constant current value. The testing wascarried out at room temperature. During the cell charging process,sodium ions are extracted from the cathode active material, and insertedinto the Hard Carbon anode. During the subsequent discharge process,sodium ions are extracted from the Hard Carbon and re-inserted into thecathode active material.

FIG. 9(A) shows the third cycle discharge voltage profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for the HardCarbon//NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.05)O₂ cell. The cathodespecific capacity corresponds to 90 mAh/g.

FIG. 9(B) shows the third cycle differential capacity profiles(Differential Capacity [mAh/g/V] Na-ion Cell Voltage [V]) for the HardCarbon//NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.05)O₂ cell. These symmetricaldata demonstrate the excellent reversibility of the ionextraction-insertion reactions in this Na-ion cell.

FIG. 9(C) shows the first four charge-discharge cycles (Na-ion CellVoltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for theHard Carbon//NaNi_(0.45)Mn_(0.45)Cu_(0.05)Ti_(0.05)O₂ cell. These datademonstrate that the level of voltage hysteresis (i.e. the voltagedifference between the charge and discharge processes) is extremelysmall, indicating the excellent kinetics of the extraction-insertionreactions.

Referring to FIGS. 10(A)-(C).

The data shown in FIGS. 10(A)-(C) are derived from the constant currentcycling data for a NaNi_(0.40)Mn_(0.40)Ca_(0.10)Ti_(0.10)O₂ activematerial in a Na-ion cell where this cathode material was coupled with aHard Carbon (Carbotron P/J) anode material. The electrolyte used is a0.5 M solution of NaClO₄ in propylene carbonate. The constant currentdata were collected at an approximate current density of 0.10 mA/cm²between voltage limits of 1.50 and 4.00 V. To ensure that the Na-ioncell was fully charged, the cell was potentiostatically held at 4.0 V atthe end of the constant current charging process until the currentdensity dropped to 20% of the constant current value. The testing wascarried out at room temperature. During the cell charging process,sodium ions are extracted from the cathode active material, and insertedinto the Hard Carbon anode. During the subsequent discharge process,sodium ions are extracted from the Hard Carbon and re-inserted into thecathode active material.

FIG. 10(A) shows the third cycle discharge voltage profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for the HardCarbon//NaNi_(0.40)Mn_(0.40)Ca_(0.10)Ti_(0.10)O₂ cell. The cathodespecific capacity corresponds to 109 mAh/g.

FIG. 10(B) shows the third cycle differential capacity profiles(Differential Capacity [mAh/g/V] Na-ion Cell Voltage [V]) for the HardCarbon//NaNi_(0.40)Mn_(0.40)Ca_(0.10)Ti_(0.10)O₂ cell. These symmetricaldata demonstrate the excellent reversibility of the ionextraction-insertion reactions in this Na-ion cell.

FIG. 10(C) shows the first four charge-discharge cycles (Na-ion CellVoltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for theHard Carbon//NaNi_(0.40)Mn_(0.40)Ca_(0.10)Ti_(0.10)O₂ cell. These datademonstrate that the level of voltage hysteresis (i.e. the voltagedifference between the charge and discharge processes) is extremelysmall, indicating the excellent kinetics of the extraction-insertionreactions.

Referring to FIGS. 11(A)-(C).

The data shown in FIGS. 11(A)-(C) are derived from the constant currentcycling data for a NaNi_(0.40)Mn_(0.40)Zn_(0.10)Ti_(0.10)O₂ activematerial in a Na-ion cell where this cathode material was coupled with aHard Carbon (Carbotron P/J) anode material. The electrolyte used is a0.5 M solution of NaClO₄ in propylene carbonate. The constant currentdata were collected at an approximate current density of 0.10 mA/cm²between voltage limits of 1.50 and 4.00 V. To ensure that the Na-ioncell was fully charged, the cell was potentiostatically held at 4.0 V atthe end of the constant current charging process until the currentdensity dropped to 20% of the constant current value. The testing wascarried out at room temperature. During the cell charging process,sodium ions are extracted from the cathode active material, and insertedinto the Hard Carbon anode. During the subsequent discharge process,sodium ions are extracted from the Hard Carbon and re-inserted into thecathode active material.

FIG. 11(A) shows the third cycle discharge voltage profile (Na-ion CellVoltage [V] versus Cathode Specific Capacity [mAh/g]) for the HardCarbon//NaNi_(0.40)Mn_(0.40)Zn_(0.10)Ti_(0.10)O₂ cell. The cathodespecific capacity corresponds to 72 mAh/g.

FIG. 11(B) shows the third cycle differential capacity profiles(Differential Capacity [mAh/g/V] Na-ion Cell Voltage [V]) for the HardCarbon//NaNi_(0.40)Mn_(0.40)Zn_(0.10)Ti_(0.10)O₂ cell. These symmetricaldata demonstrate the excellent reversibility of the ionextraction-insertion reactions in this Na-ion cell. In addition, thecharge-discharge behaviour is now largely without structure.

FIG. 11(C) shows the first four charge-discharge cycles (Na-ion CellVoltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for theHard Carbon//NaNi_(0.40)Mn_(0.40)Zn_(0.10)Ti_(0.10)O₂ cell. These datademonstrate that the level of voltage hysteresis (i.e. the voltagedifference between the charge and discharge processes) is extremelysmall, indicating the excellent kinetics of the extraction-insertionreactions.

Referring to FIG. 13(B), this shows the constant current cycling data(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for the first 4 cycles of the Na_(0.7)MnO_(2.05) (X1386) activecathode material (P2 structure) in a Na-ion cell where it is coupledwith a capacity balanced Hard Carbon (Carbotron P/J) anode material.

The electrolyte used was a 0.5 M solution of NaClO₄ in propylenecarbonate. The constant current data were collected at an approximatecurrent density of 0.20 mA/cm² between voltage limits of 1.00 and 4.20V. To ensure that the Na-ion cell was fully charged, the cell waspotentiostatically held at 4.20 V at the end of the constant currentcharging process until the current density dropped to 20% of theconstant current value. The testing was carried out at 25° C. It isevident that sodium ions are extracted from the cathode active material,Na_(0.7)MnO_(2.05), and inserted into the Hard Carbon anode during theinitial charging of the cell. During the subsequent discharge process,sodium ions are extracted from the Hard Carbon and re-inserted into thecathode active material.

The first charge process corresponds to a specific capacity for thecathode active material of only 81 mAh/g. The first discharge processcorresponds to a specific capacity for the cathode of 47 mAh/g,indicating the poor reversibility of the sodium ion extraction-insertionprocesses. Clearly the specific capacity performance for theNa_(0.7)MnO_(2.05) material (which has a P2 structure) is inferior tothe performance from the O3 cathode materials.

Referring to FIG. 14(B), this shows the constant current cycling data(Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity[mAh/g]) for the first 4 cycles of theNa_(0.95)Ni_(0.3167)Mn_(0.3167)Mg_(0.1583)Ti_(0.2083)O₂ (X1380) activematerial according to the present invention in a Na-ion cell where it iscoupled with a capacity balanced Hard Carbon (Carbotron P/J) anodematerial.

The electrolyte used was a 0.5 M solution of NaClO₄ in propylenecarbonate. The constant current data were collected at an approximatecurrent density of 0.20 mA/cm² between voltage limits of 1.00 and 4.20V. To ensure that the Na-ion cell was fully charged, the cell waspotentiostatically held at 4.20 V at the end of the constant currentcharging process until the current density dropped to 20% of theconstant current value. The testing was carried out at 25° C. It isevident that sodium ions are extracted from the cathode active material,Na_(0.95)Ni_(0.3167)Mn_(0.3167)Mg_(0.1583)Ti_(0.2083)O₂, and insertedinto the Hard Carbon anode during the initial charging of the cell.During the subsequent discharge process, sodium ions are extracted fromthe Hard Carbon and re-inserted into the cathode active material.

The first charge process corresponds to a specific capacity for thecathode active material of 228 mAh/g. The first discharge processcorresponds to a specific capacity for the cathode of 151 mAh/g,indicating the excellent active material utilization and the goodreversibility of the sodium ion extraction-insertion processes.

The invention claimed is:
 1. A compound of the formula:A_(1-δ)M¹ _(V)M² _(W)M³ _(X)M⁴ _(Y)M⁵ _(Z)O₂ wherein A is one or morealkali metals comprising sodium and/or potassium, either alone or in amixture with lithium as a minor constituent; M¹ is nickel in oxidationstate +2 M² comprises a metal in oxidation state +4 selected from one ormore of manganese, titanium and zirconium; M³ comprises a metal inoxidation state +2, selected from one or more of magnesium, calcium,copper, zinc and cobalt; M⁴ comprises a metal in oxidation state +4,selected from one or more of titanium, manganese and zirconium; M⁵comprises a metal in oxidation state +3, selected from one or more ofaluminum, iron, cobalt, molybdenum, chromium, vanadium, scandium andyttrium; wherein0≦δ≦0.1 V is in the range 0<V<0.5; W is in the range 0<W≦0.5; X is inthe range 0<X<0.5; Y is in the range 0≦Y<0.5; Z is ≧0; and furtherwherein V+W+X+Y+Z=1.
 2. A compound according to claim 1 wherein V is inthe range 0.1≦V≦0.45; W is in the range 0<W≦0.5; X is in the range0≦X<0.5; Y is in the range 0≦Y<0.5; Z is ≧0; and wherein V+W+X+Y+Z=1. 3.A compound according to claim 1 wherein V is in the range 0.3≦V≦0.45; Wis in the range 0.1≦W≦0.5; X is in the range 0.05≦X<0.45; Y is in therange 0≦Y≦0.45; Z is ≧0; and wherein V+W+X+Y+Z=1.
 4. A compoundaccording to claim 1 wherein M² M⁴.
 5. A compound according to claim 1of the formula: NaNi_(0.5−x)Mn_(0.5−x)Mg_(x)Ti_(x)O₂;NaNi_(0.5−x)Mn_(0.5−x)Mg_(x/2)Ti_(x/2)Al_(x)O₂;NaNi_(0.5−x)Mn_(0.5−x)Ca_(x)Ti_(x)O₂;NaNi_(0.5−x)Mn_(0.5−x)Co_(x)Ti_(x)O₂;NaNi_(0.5−x)Mn_(0.5−x)Cu_(x)Ti_(x)O₂;NaNi_(0.5−x)Mn_(0.5−x)Zn_(x)Ti_(x)O₂;NaNi_(0.5−x)Mn_(0.5−x)Mg_(x)Zr_(x)O₂;NaNi_(0.5−x)Mn_(0.25−x/2)Ca_(x)Ti_(0.25+x/2)O₂;NaNi_(0.5−x)Mn_(0.5)Ca_(x)O₂; NaNi_(0.5−x)Mn_(0.5−Y)Ca_(x)Ti_(Y)O₂;NaNi_(0.5−x)Ti_(0.5−x)Mg_(x)Mn_(x)O₂;NaNi_(0.5−x)Ti_(0.5−x)Ca_(x)Mn_(x)O₂;NaNi_(0.5−x)Ti_(0.5−x)Cu_(x)Mn_(x)O₂;NaNi_(0.5−x)Ti_(0.5−x)Co_(x)Mn_(x)O₂;NaNi_(0.5−x)Ti_(0.5−x)Zn_(x)Mn_(x)O₂; NaNi_(0.5−x)Mn_(0.5)Mg_(x)O₂;NaNi_(0.5−x)Mn_(0.5)Ca_(x)O₂; NaNi_(0.5−x)Mn_(0.5)Cu_(x)O₂,NaNi_(0.5−x)Mn_(0.5)Co_(x)O₂; NaNi_(0.5−x)Mn_(0.5)Zn_(x)O₂;NaNi_(0.5−x)Mn_(0.5−y)Mg_(x)Ti_(y)O₂;NaNi_(0.5−x)Mn_(0.5−y)Ca_(x)Ti_(y)O₂;NaNi_(0.5−x)Mn_(0.5−y)Cu_(x)Ti_(y)O₂;NaNi_(0.5−x)Mn_(0.5−y)CO_(x)Ti_(y)O₂;NaNi_(0.5−x)Mn_(0.5−y)Zn_(x)Ti_(y)O₂;NaNi_(0.5−x)Mn_(0.25−x/2)Mg_(x)Ti_(0.25+x/2)O₂;NaNi_(0.5−x)Mn_(0.25−x/2)Ca_(x)Ti_(0.25+x/2)O₂;NaNi_(0.5−x)Mn_(0.25−x/2)Cu_(x)Ti_(0.25+x/2)O₂;NaNi_(0.5−x)Mn_(0.25−x/2)CO_(x)Ti_(0.25+x/2)O₂;NaNi_(0.5−x)Mn_(0.25−x/2)Zn_(x)Ti_(0.25+x/2)O₂;NaNi_(0.5−x)Mn_(0.5−x)Mg_(x/2)Ti_(x/2)Al_(x)O₂;NaNi_(0.5−x)Mn_(0.5−x)Ca_(x/2)Ti_(x/2)Al_(x)O₂;NaNi_(0.5−x)Mn_(0.5−x)Cu_(x/2)Ti_(x/2)Al_(x)O₂;NaNi_(0.5−x)Mn_(0.5−x)Co_(x/2)Ti_(x/2)Al_(x)O₂;NaNi_(0.5−x)Mn_(0.5−x)Zn_(x/2)Ti_(x/2)Al_(x)O₂ andNa_(0.95)N_(0.3167)Ti_(0.3167)Mg_(0.1583)Mn_(0.2083)O₂.
 6. An electrodecomprising an active compound according to claim
 1. 7. An electrodeaccording to claim 6 used in conjunction with a counter electrode andone or more electrolyte materials.
 8. An electrode according to claim 7wherein the electrolyte material comprises an aqueous electrolytematerial.
 9. An electrode according to claim 7 wherein the electrolytematerial comprises a non-aqueous electrolyte.
 10. An energy storagedevice comprising an electrode according to claim
 6. 11. An energystorage device according to claim 10 suitable for use as one or more ofthe following: a sodium and/or potassium ion cell; a sodium and/orpotassium metal cell; a non-aqueous electrolyte sodium and/or potassiumion cell; and an aqueous electrolyte sodium and/or potassium ion cell.12. A rechargeable battery comprising an electrode according to claim 6.13. An electrochemical device comprising an electrode according to claim6.
 14. An electrochromic device comprising an electrode according toclaim
 6. 15. A method of preparing the compounds according to claim 1comprising the steps of: a) mixing starting materials together, b)heating the mixed starting materials in a furnace at a temperature ofbetween 400° C. and 1500° C., for between 2 and 20 hours to give areaction product; and c) allowing the reaction product to cool.